A side channel attack is known as a method of attacking an encryption device having an encryption processing function. The side channel attack is an attack that uses side channel information, such as power consumption, electromagnetic waves, processing time, generated during processing in the encryption device to estimate a secret key. In particular, a Differential Side-Channel Analysis (hereinafter called “DSCA”) is known as a powerful side channel attack. The DSCA performs statistical processing for a plurality of pieces of side channel information to suppress influence of noise and thereby estimates confidential information. The DSCA includes some approaches which are classified depending on the type of the side channel information used in the attack and are referred to as Differential Power Analysis (hereinafter called “DPA”) (refer to NPL 1) in the case where the power consumption is used as the side channel information and Differential Electro-Magnetic Analysis (hereinafter called “DEMA”) (refer to NPL 2) in the case where electromagnetic waves are used as the side channel information.
In the DSCA, waveform displacement or waveform noise caused during measurement of the side channel information gives significant influence on the accuracy of the attack. Thus, in order to properly perform estimation of tamper resistance of an encryption device against the DSCA, it is desirable to use side channel information that does not include the displacement or noise.
There are known, as a method of reducing influence of the displacement or noise, a Differential Frequency Analysis (hereinafter called “DFA”) (refer to NPL 4) and a phase-only correlation (refer to NPL 3).
The DFA applies Discrete Fourier Transform (hereinafter called “DFT”) to the side channel information measured in the time domain to transform the side channel information into a frequency domain to thereby calculate the intensity (power spectrum) for each frequency component and then applies the DSCA to the power spectrum. This DFA is effective for time-displacement of waveforms at the measurement time.
The phase-only correlation is a phase method that estimates displacement at the measurement time from a phase component obtained by applying the DFT to the measured side channel information with an accuracy exceeding the sampling resolution in a measuring device and corrects the estimated displacement. This phase-only correlation is effective for time-displacement of waveforms at the measurement time, as in the case of the DFA. Further, by using the phase-only correlation in combination with a low-pass filter or a band-pass filter (hereinafter called “BPF”), noise can be removed.